Wire print head

ABSTRACT

A wire printing head comprising a plurality of solenoids mounted within a frame and a plurality of spring lever arms cantilevered to the frame and having attached to the free end of the arms print wires. The print wire is moved in the direction of the medium to be printed by the movement of the solenoid armature by magnetic force in the direction of the free end of the print wire. The print wire is returned to a ready position by the spring action of the lever arm.

Unite-d StateSPat'ent 11 -1, I 1111 3,770,092

Grim 1 1 Nov. 6, 1973 I WIRE PRINT HEAD 1,271,440 6/1968 Germany 197 1 R[75] Inventor: Robert E. Grim, Joplin, Mo.

[73] Assignee: Autotronics, Incorporated, Joplin,

MQ Primary ExaminerEdgar S. Burr AttorneyRichard P. Matthews [22] F1led:Feb. 14, 1972 21 Appl. No.: 225,714

1,577,409 8/1969 France 197/l R [57] ABSTRACT [52] US. Cl. 197/1 R,101/93 C llrt. A wire rintin head com risin a luralit ofsolenoids 58Field of Search 197/1; 101/93 0 mount; with? a frame 5 z Spring leverarms cantilevered to the frame and having attached to [56] ReferencesC'ted the free end of the arms print wires. The print wire is UNITEDSTATES PATENTS moved in the direction of the medium to be printed by3,099,711 7/1963 Foley et aI. 197/1 R the movement of the solenoidarmature by magnetic 3,209,681 lO/l965 Sanbom 3,467,232 9/1969 Paige 43,603,442 9/1971 Ward 197/1 R FOREIGN PATENTS OR APPLICATIONS 1,254,38811/1967 Germany 197/1 R 2 Claims, 2 Drawing Figures force in thedirection of the free end of the printwire. The print wire is returnedto a ready position by the spring action of the lever arm.

PATENTEUNHV 61973 FIGJ TRIGGER SlGNAL .RZ Ql Q2 TYPICAL 0NE 5HOT M DRlVETRANSISTOR MULTIVI BRA [0R This invention relates to wire printingdevices, and more specifically to a wire print head.

In general, wireprinting devices are composed of individual wires thatare moved to impinge upon the medium to be printed. These devicesusually contain seven print wires and when these wires are moved toimpact a record medium printed characters are produced. It is commonpractice that electromagnetic devices such as solenoids are used to movethe wires so that the wires impinge on the medium to be printed.Usually, the wire is directly attached to the solenoid armature and thedistance that wire must be moved is equal to the distance that thesolenoid armature must be moved. The distance that the armature moves isa major factor in determining the size of the solenoid required for aparticular wire printing device. It is an object of this invention toreduce the size of the solenoid required to perform the printingfunction.

Another factor in determining the size of the solenoid is the mass thatthe solenoid must accelerate or move to impart sufficient force to theprint wire to accomplish the printing action. In past designs the sizeof the solenoid and geometric arrangement of solenoids has required thatlonger print wires (i.e. larger mass) be employed and when longer printwires are required larger solenoids are required, thus creating avicious cycle. The disadvantage of long print wires is furthercompounded by the fact that the wires bend and therefore, require thatthe armature must move a greater distance than would normally benecessary. To offset the wire flexing problem wire guides or tubes areused, but these in turn create resistance to the movement of the wireand therefore require larger solenoids. It is an object of thisinvention to reduce the length of the print wire required to perform theprinting function.

A further disadvantage of long print wires and longer distance thatsolenoid armatures must travel is that these factors increase the cyclerate of the solenoid;as the cycle rate of the solenoid is increased thesize of the solenoid must be increased to withstand temperature buildupresulting from the increased current flows required. It is an object ofthis invention to reduce the current required to perform the printingfunction.

The primary object of this invention is to provide a novel and improvedprinting head as will become apparent from the detailed description thatfollows.

To summarize the invention, it is a wire print device comprising a frameto which is cantilevered a flexible spring member. At the free end ofthe spring member is attached a print wire that travels within a wireguide that is also attached to the frame. Attached to the spring memberis a magnetizable member or armature that is located parallel to theprint wire and is moved by magnetic force in the direction of the freeend of the print wire so that the print. wire strikes the surface to beprinted. After the magnetic force is released on the armature the springaction of the flexible member returns the print wire to a readyposition.

FIG. 1 is a perspective view of the subject invention having a portioncut away to show certain inventive features.

FIG. 2 is a schematic drawing of a control curcuit suitable for use withthe subject invention.

Referring now to FIG. 1 wherein is shown printing head a preferredembodiment of the subject inven- 7 tion. The frame 1 1 is of a high heattransfering material such as aluminum or aluminum alloy or similar typematerial. The frame acts in this embodiment as to a heat sink andtherefore fins 12 are added to help dissipate the heat generated by coilassemblies 13. The coil assembly 13 comprises a body 14 that can bescrewed into the frame 1 1, a core 15 that is constructed ofmagnetizable material such as ingot iron and a coil 16 that is connectedto a control circuit such as is illustrated in FIG. 2, by terminals 17.When the coil is energized, a pole face is created at point 18 on themagnetic core 15. This pole face 18 attracts the magnetizable member 19which is attached to the flexible member 20. The magnetizable member 19can also bedescribed as an armature of coil assembly 13. The armaturecan be constructed of any well known magnetizable materials. The coilassembly 13 is also referred to herein as a solenoid. The flexiblemember 20 is attached to the frame 11 by bolts 21, only one bolt isshown in the drawing. This bolting arrangement can also be described ascantilevering the flexible member 20. At the non-bolted end of theflexible member is attached to the print wire 22. The print wire ispositioned in the wire guide 23 which is a jewel-lined cylinder. Thewire guide bearing block 24 contains seven wire guides that print wirestranslate through. The paper or ribbon, not shown, would be translatedacross the face of bearing block 24, by means not shown, and whensolenoid 13 is activated air gap 25 would be closed by the movement ofpole face 26 contained in armature 19. The air gap is quite small in thepresent invention, that is between 0.005 inches and 0.020 inches andpreferrable between 0.012 inches and 0.018 inches, because of themechanical advantage realized from employing the lever arm 20. That isto say if the distance from bolt 21 to the armature 19 is one unit andthe distance from armature 19 to print wire 22 is two units and thedistance between pole face 26and pole face 18 is denoted by dy'the printwire 22 travels a distance of 3 X dy when the air gap 25 is closed. Thisarrangement of components has the two fold advantage of reducing thesize of the solenoid required, by reducing the length of the air gap andreducing the force necessary to be imparted to the armature, and byreducing the length of theprint wire employed. A typical wire lengthuseable in the present invention is 0.75 inches with a diameter of 0.013inches. Thus, a ratio of wire length to diameter of less than 60 isreadily useable in a machine employing the subject invention, a ratiovery difficult if not impossible to provide in previously known printingmachines.

The portion of flexible member 20 from the bolt 21 to the armature 19 ismade of a spring material and imparts the spring action to this memberto return the print wire 22 to a ready position when the solenoid 13 isdeactivated. The portion of the flexible member from the armature 19 tothe print wire 22 is a light weight rigid member that acts as a leverarm. The relative light weight or low mass of this member furtherenhances the efflciency of this printing device.

The air gap or stroke of the armature can readily be adjusted by usingvarious size shims 27. As can be seen from the drawing the use of thelever arm type arrangement allows the solenoids to be grouped around thewire guide in a circular fashion, reducing the overall size of the printhead and thereby a very compact design is realized.

To control the energization of the coil 13 and thereby regulate theprinting action of the print wires, each coil 13 is connected to acontrol circuit as shown in FIG. 2,

by terminals 17. In this circuit, a trigger signal causes transistor toconduct momentarily lowering its collector potential. Capacitor Ccouples this potential drop to the base of transistor 0;, cutting itoff. The rise in collector potential of Q turns transistor Q, on throughresistor R and thus exciting coil L which is the same as coil 16 inFIG. 1. Simultaneously, transistor 0, conducts by means of resistor Rand R This electrical state is maintained until the potential at thebase of Q rises by means of charging C through R,, sufficiently to cause0;; to conduct. When 0,, conducts,

Q, is cut off and the excitation to coil 16 ceases. This type of circuitis commonly known as a one shot multivibator and is used to provideexcitation to coil 16 for a fixed period of time after the triggersignal.

By following the teachings of this invention a highly efficient wireprinter is produced that is fast acting, can be recycled at very highrates, and requires a small amount of energy for actuation.

It is to be understood that the above disclosure is by way of specificexample and that numerous modifications and variations are available tothose of ordinary skill in the art with departing from the true spiritand scope of the present invention.

I claim:

1. In a wire print device of the type having a circular frame, and aplurality of wire print assembly members mounted within said frame, witheach of said wire print assembly members comprising a solenoid having acentral core member which has a pole face at one end thereof and movablearmature means, the improvement wherein said movable armature meanscomprises b. a lightweight magnetizable member mounted on said flexibleleaf spring member,

1. said lightweight magnetizable member having a cross sectional areasubstantially equal to the cross-sectional area of the pole face on saidcentral core member,

0. and a print wire attached to the uncantilevered end of said flexibleleaf spring member, said print wire having a length to diameter ratio ofless than 60:1, said print wire being guided by a jeweled lining carriedby said frame d. said lightweight magnetizable member being mountedcloser to the cantilever mounting of said flexible spring member than tosaid print wire so as to establish a mechanical advantage for themovement of said print wire when said solenoid is actuated to effectmovement between said magnetizable member and said pole face by magneticattraction and repulsion.

2. A wire print device as defined in claim 1 wherein a closed magneticcircuit is provided for said solenoid by means of an open-toppedmagnetizable body which surrounds said central core member, saidmagnetizable body having an openings in the bottom thereof to receivesaid lightweight magnetizable member mounted on said flexible leafspring member, and said central core member being substantially T-shapedin crosssection to provide a closed magnetic path across the top of saidopen-topped magnetizable body.

1. In a wire print device of the type having a circular frame, and aplurality of wire print assembly members mounted within said frame, witheach of said wire print assembly members comprising a solenoid having acentral core member which has a pole face at one end thereof and movablearmature means, the improvement wherein said movable armature meanscomprises a. a flexible leaf spring member mounted in cantilever fashionadjacent one end thereof to said frame, said spring member extendingsubstantially radially of the frame from its point of attachment to thecenter of the device, b. a lightweight magnetizable member mounted onsaid flexible leaf spring member,
 1. said lightweight magnetizablemember having a cross sectional area substantially equal to thecross-sectional area of the pole face on said central core member, c.and a print wire attached to the uncantilevered end of said flexibleleaf spring member, said print wire having a length to diameter ratio ofless than 60:1, said print wire being guided by a jeweled lining carriedby said frame d. said lightweight magnetizable member being mountedcloser to the cantilever mounting of said flexible spring member than tosaid print wire so as to establish a mechanical advantage for themovement of said print wire when said solenoid is actuated to effectmovement between said magnetizable member and said pole face by magneticattraction and repulsion.
 2. A wire print device as defined in claim 1wherein a closed magnetic circuit is provided for said solenoid by meansof an open-topped magnetizable body which surrounds said central coremember, said magnetizable body having an openings in the bottom thereofto receive said lightweight magnetizable member mounted on said flexibleleaf spring member, and said central core member being substantiallyT-shaped in cross-section to provide a closed magnetic path across thetop of said open-topped magnetizable body.